Once-through vapor generator



Feb. 6, 1962 H. BEYERLEIN 3,019,774

ONCE-THROUGH VAPOR GENERATOR Filed Sept. 16. 1959 INVENTOR. Herbert Beyerlein 5 ATTORNEY the remainder of the heating surfaces.

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This invention relates in general to forced flow, oncethrough vapor generating units and more particularly to apparatus for starting up and shutting down forced flow, once-through vapor generators.

In starting up and shutting down forced flow, oncethrough vapor generators it is important to use care in controlling the way in which the sections of the unit exposed to hightemperatures are heated or cooled to avoid any damage resulting from extreme difiere ntial thermal Stresses. Further, it is also important to avoid the deposition of solids within these portions of the unit to prevent tube failure due to'overheating resulting from the presence of the deposited solids.

In the past, it has beenproposed to place a flash drum and shut-off valve'between the primary and secondary superheaters so that the heating surfaces which they separate could be started up independently. The flash drum arrangement, however, is disadvantageousv due both to {the cost of the heavy plate required and the size of the drum which substantially increases the size and cost of the vapor generator. The present invention avoids these disadvantages by providing a simple and relatively inex- 1 atet denser 42.

pensive arrangement which permits the secondary superheater to be heated or cooled during starting-up or shutting down operations, respectively, independently from It is, therefore, the object of this invention to provide apparatus whereby the secondary superheater may be separately heated or cooled during starting-up or shutting.- down, respectively, of the vapor generators, and in addition, to provide that only steam is permitted to flow through the secondary superheater.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of the invention.

The invention will be described in greater detail with reference to the accompanying drawing which is a schematic showing of the arrangement of the apparatus in the present invention. In the drawing a forced flow, once-through vapor generator 10 receives a fiow of heating gases from a burner 11. Feed water is supplied to the vapor generator 10 from the feed water ta'nk12 by means of a feed water pump 14. e v,

The flow of feed water to the vapor generator 10 .is controlled by an inlet valve 16 and under normal operating conditionsit flows serially through an economizer section 13, a vapor generating section 2i), a primary superheater 22 and a secondary superheater 24. The primary superheater 22 and secondary superheater 24 are connected by means of a main flow passageway 26. A shutoff valve 28 is located in the main flow passageway 26 to close off fiow into the secondary superheater. A conduit 30 supplies a by-pass around the shut-off valve to permit the flow of heated feed water from the primary to the secondary superheater when the valve 28 is closed. A valve 31 is located in the by-pass conduit 30 to regulate the amount of flow passing therethrough.

The secondary superheater 2.4 is connected to a turbine 32 by means of an outlet passageway 34. An outlet valve 36 is disposed in the passageway 34 to govern the flow of superheated steam to the turbine 32. A first take-off conduit 40 is connected at one end to the flow passageway 26 upstream from the valve 28 and at its other end to a condenser 42. A valve 44 is positioned in the conduit 40 to regulate the flow therein. A second take-oft conduit 46 is connected at one end to the flow passageway 34 and at its opposite end to the condenser 42. A valve 48 controls the flow through this second take-0E conduit to the condenser.

The method of starting up the once-through vapor generator of the. present invention is carried out in the following manner: first, the valve 28 in the main fiow passageway 26, the valve 31 located in the by-pass conduit 30 and the outlet valve 36 are closed and the valves 44 and 48 in the first and second take-01f conduits 40 and 46, respectively, are opened. Next, the feed water pump 14 is started upand the'amount of feed water delivered to the vapor'generator is regulated by means of the inlet valve 16and the delivery of heating gases to the heating surfaces is commenced. With the valves arranged in this manner, the feed water absorbs heat as it circulates through the economizer section 16, the vapor generating s'ection ls, and the primary superheater 20 and then passes 01? through the take-off conduit 40 to the con- From the condensenthe feed water returns to'the feed water tank- 12 to complete the circuit. The pressure required for this portion of the starting-up operation is achieved by regulating the valve 44 in the first take-off conduit 40.

When the circulation through primary superheater has reached the desired pressure and temperature, the quantity of heating gases are increased and valve 31 in by-pass conduit 3tlis opened slightly to admit a small quantity of the heated feed water under pressure to the secondary superheater 24. Since the valve 48 is open, there is no pressure maintained in the secondary superheater and a valve. Since the temperature and pressure of the feed waterin the portion of the vapor generator upstream of the valve has been regulated it is possible to maintain the feed water in a vapor state within the secondary superheater. In this manner, by maintaining differential pressure across the valve 31, it is possible to assure the presence of steam within the secondary superheater at all times. In this way, the final vaporization occurs before the feed water enters the secondary superheater and the possibility of any deposition of solids therein is avoided.

As the amount of heating gases delivered to the vapor generator is increased, the temperature of the feed water rises and the valve 31 is opened wider to permit additional flow to the secondary superheater 24. At the same time, the valve 48 in the second take-off conduit 'is regulated to maintain the pressure drop across the valve 31 in the by-pass conduit. When the steam temperature on either side of the valve has been equalized the pressure in the secondary superheater 24 is, adapted to that in the primary superheater '22 by regulating the valve 48. At this, point in the starting-up operation, the valve 28 in the main flow passageway 26 is opened and the valve '31 in the by-pass conduit and the valve 44 in the first take-off conduit 40 are closed. When the desired starting-up temperature and pressure have finally een achieved, the regulating valve 48 is closed and the outlet valve 36 leading to the turbine 32 is opened and the once-through vapor generator is ready for operation.

In the shutting-down procedure for the forced flow, once-through vapor generator of the present invention, the temperature and pressure of the vaporizable fluid is regulated to properly cool the secondary superheater surfaces and to avoid the deposition of solids therein. After lowering the steam capacity and the superheated steam temperatures as much as possible, the shutting,- down procedure is as follows: first, the valve 48 in the second take-off conduit is opened and the outlet valve 36 is closed thereby shutting off the flow of superheated vapor to the turbine. Next, the valve 44 is opened gradually and the valve 48 is regulated to maintain the pressure within the secondary superheater. The heated feed water now flows through the first and second take-elf conduits, 40, 46 to the condenser 42. With the flow arranged in this way, the flow of heating gases over the heating surfaces is discontinued and the valve 28 in the main flow passageway 26 is closed and the flow to the secondary superheater is admitted by Way of the valve 31. By adjusting valve 48 the pressure in the secondary superheater is lowered and a pressure differential is maintained across the valve 31 so that only vapor is, admitted to the secondary heater. When the secondary superheater surfaces have been sulficiently cooled flow therethrough is discontinued by closing valves 31, '48.

Now the operating medium flows through the vapor generator as far as the primary superheater 22 and then off through the take-off conduit 40 to the condenser 42. When these surfaces have been sufficiently cooled, the feed water pump 14 is turned off and the shutting-down operation is completed. In both the starting-up and shutting-down operations the deposition of solids is avoided within the secondary superheater surfaces and the heating or cooling of these high temperature surfaces is controlled to avoid any failures resulting from excessive differential thermal stresses.

While in accordance with the provisions .of the statutes I have illustrated and described herein the best form and mode of operation of the invention now known to me those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by my claims, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

What is claimed is:

1. A method of starting up a forced flow once-through vapor generator having first heating surfaces including a primary superheatcr and second heating surfaces including a secondary superheater serially connected therein, a point of use connected to said second heating surfaces, a vaporizable fluid flowing through said first and second heating surfaces wherein it is vaporized and superheated by the passage of heating gases thereover so that only vapor flows through said second heating surfaces, the invention comprising starting up with the flow of said vaporizable fluid through only said first heating surfaces and then condensing and recirculating it while commencing the passage of heating gases over said first and second heating surfaces, heating said vaporizable fluid as it flows through said first heating surfaces to a selected temperature and pressure, gradually increasing the flow of hen ing gases over said first and second heating surfaces, bypassing a portion of said vaporizable fluid from said first heating surfaces to said second heating surfaces, throttling said portion of said vaporizable fluid entering said second heatingsurfaces sothat it flashes into a vapor, condensing and recirculating the vapor flowing through said second heating surfaces progressively increasing the flow of vaporizable fluid from said first heating surfaces to said second heating surfaces indirect relationship to said increase in heating gas flow to maintain only vapor flowing through said second heating surfaces until the desired conditions of temperature and pressure for starting the unit are attained, admitting the flow of vaporizable fluid directly from said first heating surfaces to said second heating surfaces and discontinuing lay-passing said vaporizable fluid from said first heating surfaces to said second heating surfaces, passing the vapor from said second heating surfaces to said point of use, and at the same time discontinuing the flow from said first and second heating surfaces to be condensed and recirculated.

2. A method of shutting down a forced flow oncethroug h 'vapor generator having first heating surfaces including a primary superhcater and second heating surfaces including a secondary superheater serially connected therein, apoint of'use connected to said secondjheating surfaces,a v'a orizablefiuid flowing through said first and second heating surfaces wherein it is vaporized and superheated by the passage of heating gases thereover so that only vapor fl'ows through said second heating surfaces, the "invention comprising shutting off the flow of said vaporizable fluid to said point of use, condensing and recirculating the flow of "said vapo'rizabl'e fluid from both said firstand second heating surfaces, regulatingthe flow withdrawn from said second heating surfaces to maintain "only vapor flowing 'ther ethrough while shutting off the flow of said vaporizable fiuid from said first heating surfaces directly to said second heating surfaces and at the same time lay-passing a portion of the flow of said vapori zable fluid passing through said first heating surfaces to said second heating surfaces so that only vapor enters the second heating surfaces, suspending the passage of heating gases over said heating surfaces, discontinuing the by-pass flow of said vaporizable fluid to said second heating surfaces when said second heating surfaces are sufliciently cool and subsequently discontinuing flow of said 'va-porizable fluid to said first heating surfaces when said I first heating surfaces are sufiiciently cool to shut down operation of the once-through vapor generator.

3. A forced flow once-through vapor generator having a vaporizab'le fluid flowing thereth'rough to be vaporized and superheated comprising first heating surfaces including a primary superheater, second heating surfaces including a secondary superheater serially connected to and receiving vaporizable fluid from said first heating surfaces, a valve for shutting off flow of said vaporizable fluid from said first heating surfaces to said second heating surfaces, a bypass conduit connecting said first and second heating surfaces around said valve, means located in said by-pass conduit for expanding vaporizable fluid flowing therethrough from said first heating surfaces so that only vapor enters said second heating surfaces, means for flowing said vaporizable fluid from said first heating surfaces to be condensed and recirculated, and means for flowing vapor from said second heating surfaces to be condensed and recirculated.

References Cited in the file of this patent v UNITED STATES PATENTS 2,858,807 Strange Nov.- 4, 1958 2,901,887 Burt Sept. 1, 1959 FOREIGN PATENTS 941,291 Germany Apr. 5, 1956' UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 3,019,774 February 6, 1962 Herbert Beyerlein It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

In the grant lines 2 and 12, and in the heading to the printed specification, line 4, for "Dunwerke", each occurrence read Durrwerke column 4t line 62, name of inventor for "Strange" read Stange Signed and sealed this 31st day of July 1962..

SEA Att est: L)

ERNEST w. SWIDER DAVID LADD Attestiug Officer Commissioner of Patents 

